Although up to 95% of patients survive hospitalization following MI, many of these patients will develop chronic heart failure due to extensive damage to heart muscle, resulting in 50% mortality at five years post-MI and a huge economic burden. One chief cause of heart failure is cardiomyocyte death post-MI, which is part of the left ventricular remodeling process that leads to replacement of functional tissue with a dense, fibrotic scar. Due to the inability of cardiomyocytes to effectively re-enter the cell cycle and proliferate, controlled induction of cardiomyocyte proliferation is an emerging and important goal for therapies aimed at improving outcomes after MI. Murine studies have shown that cardiac administration if microRNA 302 (miR302, a natural inhibitor of Hippo signaling) in a gel formulation allowing for release of the RNA over 1 week leads to vastly decreased scar size and improved cardiac function following ischemia/reperfusion. This approach to cardiac regeneration is compelling by combining the simplicity of local administration of a single molecule at a single timepoint with the ability of miR302 to profoundly, but transiently affect the developmental state of cardiomyocytes: under the action of miR302, in situ adult cardiomyocytes de-differentiate to an earlier, proliferative state. As miR302 is rapidly degraded once released from the formulation, the cells revert to adult, fully functional cardiomyocytes after an initial phase of proliferation. Thus, by interfering with a series of coordinated pathways, miR302 confers the cardiac regenerative property of lower vertebrates (e.g. zebrafish) to the murine heart. Prolifagen is developing a microRNA mimic (miR302, administered as a single intracardiac injection in a gel formulation) to induce cardiac regeneration after myocardial infarct (MI) and thus prevent cardiac remodeling and heart failure. Our SBIR phase I proposal will test the hypothesis that local miR302/hydrogel treatment is able to drive cardiomyocyte proliferation covering the extended area of cardiac damage in a pig model of ischemia/ reperfusion, as a proof-of-concept enabling clinical trial decision. In addition, exploration of the proliferative response at 2 timepoints after myocardial infarction will allow to best define the optimal patient population for clinical development. By reducing the number. of patients with heart failure subsequent to myocardial infarction, a successful product will have a huge public health impact, keeping patients independent and avoiding hospitalizations, costly heart transplants and death.